The present invention generally relates to a process for the reclamation and reuse of semiconductor material substrates, especially silicon wafers, in the manufacture of electronic components.
During the course of the manufacture of integrated circuits and other semiconductor devices, batches of silicon wafers are occasionally improperly processed. For example, a batch of silicon wafers may be given an improper ion-implantation step or incorrectly processed photolithographically. As a result, these wafers in their then current state are no longer suitable for the manufacture of semiconductor devices. Rather than simply disposing of these batches of wafers, it has been proposed that they be reclaimed for reuse in the semiconductor device manufacturing process.
Reclaiming a silicon wafer for reuse generally requires the removal of any layers which may have been deposited on the wafer surface as well as a portion of the original wafer, typically several to a few tens of micrometers of the wafer. Typically, these layers are removed by chemical-mechanical polishing of the surface(s).
Because of the uncertainty that reclaimed wafers are equivalent to virgin “prime” wafers and are suitable for use as a substrate in the manufacture of semiconductor devices, reclaimed wafers have generally been restricted to use as mechanical “dummy” or monitor wafers. A primary concern is the presence of oxygen precipitates in what will become the device layer of such re-claimed wafers.
Thermal treatment cycles typically employed in the fabrication of electronic devices can cause the precipitation of oxygen in silicon wafers which are supersaturated in oxygen. Depending upon their location in the wafer, the precipitates can be harmful or beneficial. Oxygen precipitates located in the active device region of the wafer can impair the operation of the device. It is required, therefore, that the wafer contain an oxygen precipitate free zone (or “denuded zone”) of a predetermined depth in the near-surface region of the wafer with the actual depth required for a given application depending upon the design of the device. Oxygen precipitates located in the bulk of the wafer, however, are capable of trapping undesired metal impurities that may come into contact with the wafer. The use of oxygen precipitates located in the bulk of the wafer to trap metals is commonly referred to as internal or intrinsic gettering (“IG”). For many applications, therefore, it is preferred that the wafer contain oxygen precipitates in the wafer bulk, that is, the region of the wafer outside the device layer.
Historically, electronic device fabrication processes included a series of steps which were designed to produce a precipitate free zone with the balance of the wafer, i.e., the wafer bulk, containing a sufficient number of oxygen precipitates for IG purposes. Denuded zones have conventionally been formed, for example, in a high-low-high thermal sequence such as (a) oxygen out-diffusion heat treatment at a high temperature (>1100° C.) in an inert ambient for a period of at least about 4 hours, (b) oxygen precipitate nuclei formation at a low temperature (600–750° C.), and (c) growth of oxygen (SiO2) precipitates at a high temperature (1000–1150° C.). See, e.g., F. Shimura, Semiconductor Silicon Crystal Technology, Academic Press, Inc., San Diego Calif. (1989) at pages 361–367 and the references cited therein.
More recently, advanced electronic device manufacturing processes such as DRAM manufacturing processes have begun to minimize the use of high temperature process steps. As a result, there is a certain, often considerable, amount of variability in the distribution of oxygen precipitates which develop in wafers subjected to a defined integrated circuit manufacturing process. This variability, combined with the fact that reclaimed wafers may be obtained from any arbitrary point in the semiconductor device manufacturing process has been, at least in part, responsible for restricting reclaimed wafers to monitor wafer uses; as noted above, the semiconductor device manufacturing process requires that the wafers reliably have a oxygen precipitate free zone of adequate depth and, to date, reclaimed wafers could not be expected to reliably provide a precipitate free zone in what will become the device layer.